WASHINGTON — President Barack Obama has opened clear leads over Republican presidential contender Mitt Romney in three vital states, new polls found Wednesday, in a scenario likely to see him re-elected if repeated in November.

Surveys of Florida, Ohio and Pennsylvania by Quinnipiac University and the New York Times and CBS News showed the Democratic president breaking the 50 percent barrier, less than 100 days before November’s election.

Large numbers of those polled saw Romney unfavorably, in a worrying sign for the presumptive Republican nominee.

“If today were Nov. 6, President Barack Obama would sweep the key swing states of Florida, Ohio and Pennsylvania and — if history is any guide — into a second term,” said Peter Brown, assistant director of the Quinnipiac University Polling Institute.

No candidate since 1960 has won the White House without winning two of the trio.

While independent voters break strongly for Obama in Pennsylvania, a state that Romney has been trying to make more competitive, they are closely split in Florida and Ohio. Of the coalition that Obama built to win the White House, independent voters remain a hurdle, with a little more than half in Florida and Ohio saying they disapprove of his job performance.

But a torrent of television advertising in the states, particularly in Ohio and Florida, appears to be resonating in Obama’s quest to define his Republican rival. The polls found that more voters say Romney’s experience was too focused on making profits at Bain Capital, the private equity firm he led, rather than the kind of experience that would help create jobs.

The polls found that Obama faces substantial hurdles of his own, most of them rooted in the electorate’s deeply pessimistic outlook on the economy.

By double-digit margins, voters in each state say his policies would hurt, rather than help, their personal financial situation if he won re-election, a worrisome sign considering the economy is ranked as voters’ chief concern.

“Regardless of who gets in, neither one of them can do much about the economy, because it’s bigger than what one man can do, no matter what his policies are,” said William Basler, 69, an independent voter and a financial adviser from Fort Myers, Fla. “I think Romney has a little more economic experience because of his business background than Obama does, but I’m voting for Obama because his policies are more in line with my thinking overall.”

Likability can also be an important indicator of a candidate’s electoral performance, and Romney’s poor showing on this may concern his campaign. Some 42% of Florida voters, 43% of Ohioans and 47% of Pennsylvanians said they had an unfavorable opinion of him.

The president drew broad support from voters in each state for a proposal to raise income taxes on people whose household income is more than $250,000. The plan received the backing of 58 percent of likely voters in Florida, 60 percent in Ohio and 62 percent in Pennsylvania.

The state polls were conducted by telephone, both land lines and cellphones, from July 24 through July 30 among 1,177 likely voters in Florida, 1,193 likely voters in Ohio and 1,168 likely voters in Pennsylvania.